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What is the best approach to get the Map Output keys to a reducer in reverse order? By default the reducer receives all keys in ascending order of keys. Any help or comments widely appreciated.
In simple words, in the normal scenario, if a map emits keys 1,4,3,5,2 the reducer receives the same as 1,2,3,4,5. I would like the reducer to receive 5,4,3,2,1 instead.
In Hadoop 1.X, you can specify a custom comparator class for your outputs using
JobConf.setOutputKeyComparatorClass.Your comparator must implement the
RawComparatorinterface.With Hadoop 2.X, this is done by using
Job.setSortComparatorClass, still with an implementation ofRawComparator.